1. Field of the Invention
This invention relates to a process for sterilizing a articles and more specifically to a method and apparatus for sterilizing articles by subjecting them to one or more rapid temperature changes.
2. Description of Related Art
Several years ago the process of sterilizing different articles, particularly medical devices, involved immersing the articles in a disinfectant or inserting the articles into an autoclave. Gas sterilization and irradiation processes have has subsequently been introduced, but with only limited acceptance. Ethylene-oxide, for example, is a disinfecting gas, but has been classified as a carcinogen and mutant. Apparatus required for irradiation can subject workers and the environment to safety hazards.
U.S. Pat. No. 5,213,759 (1993) to Castberg et al. discloses a sterilizing method utilizing ultraviolet radiation. Apparatus directs UV energy to a surface immersed in an inert gas to render micro-organisms non-viable.
U.S. Pat. No. 5.,223,217 (1993) to Frizziero discloses a sterilization process by which a device for filling syringes is subjected to washing and sterilizing steam. A sterile gas, such as sterile nitrogen, is supplied after the steam sterilization process elevates the temperature to a predetermined value. This sterile gas remains in contact with all the sterilized surfaces until subsequent use.
U.S. Pat. Nos. 4,976,920 (1990), 5,171,525 (1992) and 5,200,158 (1993) to Jacob disclose methods and apparatus for dry sterilization of medical devices. In accordance with these methods, items to be sterilized are located in a vacuum chamber that has a nominal operating pressure of less than 1 torr. RF energy supplied to a coil within the cavity produces a discharge with hydrogen or oxygen as a reducing or oxidizing gas respectively. The interaction with the excited molecular and atomic species formed by this interaction produces low temperature plasma that sterilizes items it contacts.
Related U.S. Pat. Nos. 5,115,166 (1992) to Campbell et al., 5,178,829 (1993) to Moulton et al. and 5,186,893 (1993) to Moulton et al. disclose the use of plasma for sterilization. Generally each of these patents discloses sterilization by exposure of an article to a plasma generated from a gas mixture that can be argon, helium, nitrogen or mixtures thereof with a mixture of hydrogen or oxygen. The plasma is generated in a vacuum chamber with an operating pressure of less than 10 torr for a time period sufficient to effect sterilization. In U.S. Pat. No. 5,178,829, in particular, the process is modified to provide gas sterilization by subjecting articles to the gas plasma until the temperature in the sterilizing chamber rises to a preselected maximum. The flow of plasma gas to the sterilizing chamber then terminates until the temperature in the sterilizing chamber falls below a preselected value. These steps repeat until sterilization is effected. The pressure in the chamber varies from 0.1 to 10 torr.
Each of the foregoing sterilization methods operate effectively. However, the use of special gases introduces a requirement for obtaining and handling those gases in the operating environment. The RF sources used in certain of these processes particularly for generating plasmas and ultraviolet energy, must be properly shielded in order to avoid disturbance of any proximate RF-sensitive equipment. These plasma processes also operate in a so-called high vacuum range of 10 torr or less that may require special chambers and vacuum pumping systems. After the sterilization process is completed, care must be taken of disposing of residual gases particularly where significant quantities of ionized gas may be present.